This invention relates to ultrasonic diagnostic imaging and, in particular, to spatially compounded three dimensional ultrasonic imaging systems and methods.
Co-pending U.S. patent applications Ser. No. 09/335,058 and 09/435,118 describe apparatus and methods for performing real time spatial compounding of ultrasonic diagnostic images. Spatial compounding is an imaging technique in which ultrasound image data of a given target that has been obtained from multiple vantage points or look directions are combined into a single compounded image by combining the data for example by linearly or nonlinearly averaging or filtering. The compounded image typically shows lower speckle and better specular reflector delineation than conventional ultrasound images produced from a single look direction.
A number of techniques have been proposed in the literature for extending the application of spatial compounding to three dimensional (3D) volumetric ultrasound image data. Three dimensional image data can benefit from spatial compounding, as the speckle reduction and better reflector delineation can improve the ability to better render a three dimensional image, since clutter effects can debilitate the 3D rendering process. At one end of the 3D spatial compounding spectrum is the acquisition of the image data by a large, static two dimensional ultrasonic transducer array as described for example in U.S. Pat. No. 5,653,235. As mentioned in this patent, if the two dimensional array can electronically steer ultrasound beams widely over a volumetric region, spatially compounded 3D images can be acquired without the need for the operator to move the probe physically. However, such a fully electronically controlled and physically motionless system requires tremendous technological sophistication and is not yet commercially feasible. At the other end of the spectrum are the systems and techniques described by Moskalik et al. and Rohling et al. in xe2x80x9cRegistration of Three-dimensional Compound Ultrasound Scans of the Breast for Refraction and Motion Correction, A. Moskalik et al., Ultrasound in Med. and Biol., vol. 21 no. 6, pp 769-78 (1995) and xe2x80x9cAutomatic Registration of 3-D Ultrasound Images, R. Rohling et al., Ultrasound in Med. and Biol., vol. 24 no. 6, pp 841-54 (1998). These techniques involve much less sophisticated systems and operate by acquiring sequential planes of ultrasonic images as the operator moves a 1D transducer array across the patient""s body. In second and subsequent scans the orientation of the transducer probe with respect to the body is changed by tipping or tilting the probe differently each time. Each scan thereby acquires a sequence of ultrasound images at a different orientation. The images from the different scans are then combined after being registered, usually by the use of a position sensor attached to the transducer probe. While requiring far less complex equipment as compared to the fully electronically steered approach, the performance of multiple scans to acquire image data for compounding makes the technique susceptible to motional effects and registration inaccuracies. Such problems can introduce blurring into the image data, which can adversely affect the 3D image rendering process. It would be desirable to take an intermediate approach which does not have the complexity and attendant cost of the fully electronically steered approach but avoids the inaccuracies introduced by the multiple scan approaches.
In accordance with the principles of the present invention apparatus and techniques are provided for producing spatially compounded three dimensional ultrasonic images. Scanning is performed by moving a probe to scan a three dimensional volume of the body. As the probe is moved, multiple scans are performed electronically in different look directions. At the end of a single scan image data is provided from multiple look directions of a target so that a spatially compounded three dimensional image can be formed. By acquiring the multiple look directions in a single scan, motional effects and the need for intensive registration processing are significantly reduced. Multiple scans can be performed and compounded, which increase the speckle reduction as a function of the product of the number of scans and look directions.